Exploiting their characteristics, reverse osmosis membranes are practically used for desalination, concentration, and the like in various applications. It is known that, in order to prevent reduction in the permeation flux and salt rejection of a reverse osmosis membrane, the reverse osmosis membrane is brought into contact with poly(vinyl alcohol) (PVA) (Patent Documents 1 to 3 cited below). A reverse osmosis membrane brought into contact with PVA becomes hydrophilic and maintains its permeability.
Since poly(vinyl alcohol) (PVA) has many OH groups and is highly hydrophilic, the adsorption of PVA to a reverse osmosis membrane reduces the adsorption of proteins on the reverse osmosis membrane and improves the fouling resistance of the reverse osmosis membrane.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 51-13388    Patent Document 2: Japanese Unexamined Patent Application Publication No. 53-28083    Patent Document 3: Japanese Unexamined Patent Application Publication No. 11-28466